Undefined PHP variable, How to fix this?

Question

1.00/5 (1 vote)

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I have a PHP file It is like this:

PHP

<?php
$myFile = "chat.txt";
$fh = fopen($myFile, 'a') or die("can't open file");
$stringData = $_POST['uname']. ": ";
fwrite($fh, $stringData);
$stringData = $_POST['msg']. "<br>";
fwrite($fh, $stringData);
fclose($fh);
?>
<!DOCTYPE html>
<html>
<head>
<div id="php">
</div>
<link rel="stylesheet" type="text/css" href="style.css"> 
<title>Red Army | Chat Room</title>
</head>
<body bgcolor="darkred">
<div id="header">
<h1 align="center">
The Red Army
</h1><br>
<h2 align="center"><a href="mems.php">Members</a>    <a href="app.php">Applications</a>    <a href="news.php">News</a>    <a href="about.php">About</a>    <a href="other.php">Other</a>
</div>
<div id="main">
<p align="center">
<div id="chatbox" class="boxed">
<?php
$myFile = "chat.txt";
$fh = fopen($myFile, 'r');
$theData = fread($fh, filesize($myFile));
fclose($fh);
echo $theData;
?>
</div>
<form action="?" method="post">
Username: <input type="text" name="uname"><br>
Message: <input type="text" name="msg">
<input type="submit">
</form>
<br>
<br>
<!--Ending-->
<br>
<br>
<br>
<br>
<font size="1">Coded and Founded by Jayden S</font>
<!--Ending-->
</p>
</div>
</body>

I get the undefined variable error and I cant set a post variable or it just comes out whatever I set it to. So how do I get the error be hidden or solve the error? The contents of chat.txt are nothing but the file does exist. If you can help me that would be great.

Thanks for reading!

Posted 6-Jul-13 7:22am

G4mm4R4y

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Comments

Sergey Alexandrovich Kryukov 6-Jul-13 13:24pm

In what line?
Anyway, don't use undefined variables... :-)
—SA

G4mm4R4y 6-Jul-13 13:50pm

Not sure what line I will run the page again but the undefined variables? That's what I am asking how can I NOT use undefined variables there It may be a dumb question but I am new to php. Maybe im jumping into things. But I am trying to basically make a chat box and the variables aren't defined how do I make it wait till they are defined to run that code?

G4mm4R4y 6-Jul-13 13:53pm

( ! ) Notice: Undefined index: uname in C:\wamp\www\chat.php on line 4

Call Stack

#

Time

Memory

Function

Location

1 0.0015 249456 {main}( ) ..\chat.php:0

( ! ) Notice: Undefined index: msg in C:\wamp\www\chat.php on line 6

Call Stack

#

Time

Memory

Function

Location

1 0.0015 249456 {main}( ) ..\chat.php:0

This is the error report

Sergey Alexandrovich Kryukov 6-Jul-13 14:03pm

There is no "wait". How? PHP works when something is already posted. Here is the thing: I cannot see with unarmed eye where the undefined variable is. You need to develop some debugging techniques. You really need to investigate which undefined variable actually used and where. In particular, you can use try-catch blocks just for investigation (http://php.net/manual/en/language.exceptions.php). I also used to use Phalanger to develop fragments of code under the debugger of Visual Studio...
—SA

G4mm4R4y 6-Jul-13 14:07pm

The undefined variables are "$_POST['msg']" and "$_POST['uname'] I know there is a way no offense to your knowledge, because I found a tutorial that let me do this I believe you use javascript but I feel there is an easier way, but the chat box works it just displays the error message which is not very user friendly to my website. The action="?" uses the same page as the action. Can I hide the error message or fix it in any way? I don't want to have to make another page, as my hosting plan has limited space.

EDIT:
The undefined variable is the first script seen trying to append chat.txt

Sergey Alexandrovich Kryukov 6-Jul-13 14:20pm

Thank you for the clarification.

You can hide exceptions via try-catch, but it's too bad to hide anything. Generally, the PHP installed on HTTP server in production should ultimately hide all exceptions, but you need to reveal them, not hide. :-)

OK, I think I can see the problem. Probably, you have two different situations: 1) when your HTTP request comes to some page as a result of POST, 2) when the same page is simply loaded from URL.

—SA

G4mm4R4y 6-Jul-13 14:26pm

Im offline right now for testing but here is an example
http://localhost/chat.php --This is what I load.
http://localhost/chat.php? --This is when I hit send
The message appears but that isn't the problem.
The undefined variable is Did that answer anything you said? Im not sure. This was the number 2 situation I don't understand the number one,

Sergey Alexandrovich Kryukov 6-Jul-13 15:28pm

You don't need this question mark at the end of URL. You need to detect if the post is done or not trough the post results themselves.
Number one is this: your form's action attribute means that the form submit sends an HTTP request with the URL specified in that attribute and also it includes the post parameters with keys "uname" and "msg". If one simply loads http:/localhost/chat.php, it does the same, but without sending post parameters. Therefore, they remain undefined; this is the second case...
—SA

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Sergey Alexandrovich Kryukov · Accepted Answer · 2013-07-06T08:23:00

Solution 1

Please see my comments to the question. You probably use the same page for showing the form and for showing the result of post. You just need to design your code to appropriately take these both possibilities into account.

In particular, you can use the very fact that $_POST["someKey"] is undefined by testing it: http://php.net/manual/en/function.isset.php[^].

—SA

Posted 6-Jul-13 8:23am

Sergey Alexandrovich Kryukov

Updated 6-Jul-13 8:24am

v2

Comments

G4mm4R4y 6-Jul-13 14:46pm

Ill accept this but still confused this is the best help I could get. But basically what I got was "Hey just make a new page!" So I will.

Sergey Alexandrovich Kryukov 6-Jul-13 15:27pm

Great. You see, you just need to thoroughly design your code. Make a new page is the easiest approach. You can have one page with the form and another with the post results. However, reusing the same page for both form and post result is quite possible and is most usually used. On postback, you also need to create the same very form, but populate it with the values obtained from the latest post.
—SA